1. The Field of the Invention
The present invention relates generally to medical devices and methods of use for closing tissue openings such as patent foramen ovale (“PFO”). More particularly, the present invention relates to devices, systems, and methods for closing a PFO by applying radio frequency (“RF”) energy to the tissue in and/or around the PFO and for determining an RF dosage to be applied to the tissue.
2. The Relevant Technology
Physical malformations or defects that are present at birth can be detrimental and even lethal when left uncorrected. A PFO is an example of a cardiac birth defect that can be problematic and even result in death when combined with other factors such as blood clots or other congenital heart defects. A PFO occurs when an opening between the upper two chambers of the heart fail to close during or after birth. This birth defect is sometimes also known as a “hole in the heart.”
Some of the problems associated with a PFO can occur when a blood clot travels between the left and right atria of the heart through the PFO, and ends up on the arterial side. A blood clot in the left atrium can be passed through the aorta and travel to the brain or other organs, and cause embolization, stroke, or a heart attack. A PFO can be treated by being closed by a surgical procedure. Additionally, other similar defects (e.g., septal or otherwise) where some tissue needs to be closed in order to function properly can include the general categories of atrial-septal defects (“ASDs”), ventricular-septal defects (“VSCs”) and patent ductus arterosus (“PDA”), and the like.
FIGS. 1A-1C depict various views of a heart having a PFO. The heart 10 is shown in a cross-section view in FIG. 1A. In a normal heart 10, the right atrium 30 receives systemic venous blood from the superior vena cava 15 and the inferior vena cava 25, and then delivers the blood via the tricuspid valve 35 to the right ventricle 60. However, in the depicted heart 10 a septal defect, which is shown as a PFO 50, is present between right atrium 30 and left atrium 40.
The PFO 50 is depicted as an open flap on the septum between the heart's right atrium 30 and left atrium 40. In a normal heart 10, the left atrium 40 receives oxygenated blood from the lungs 40 via pulmonary veins 75, and then delivers the blood to the left ventricle 80 via the bicuspid valve 45. In a heart 10 having a PFO 50 some systemic venous blood also passes from the right atrium 30 through the PFO 50 and mixes with the oxygenated blood in left atrium 40, and then is routed to the body from left ventricle 80 via aorta 85.
During fetal development of the heart 10, the interventricular septum 70 divides the right ventricle 60 and left ventricle 80. In contrast, the atrium is only partially partitioned into right and left chambers during normal fetal development, which results in a foramen ovale fluidly coupling the right and left atrial chambers. As shown in FIG. 1B, when the septum primum 52 incompletely fuses with the septum secundum 54 of the atrial wall, the result can be a tunnel 58 depicted as a PFO 50, or an ASD (not shown).
FIG. 1C provides a view of the crescent-shaped, overhanging configuration of the septum secundum 54 from within the right atrium 30 in a heart 10 having a PFO 50. The septum secundum 54 is defined by its inferior aspect 55, corresponding with the solid line in FIG. 1C, and its superior aspect 53 represented by the phantom line, which is its attachment location to the septum primum 52. The septum secundum 54 and septum primum 52 blend together at the ends of the septum secundum 54. The anterior end 56a and posterior end 56p are referred to herein as “merger points” for the septum secundum 54 and septum primum 52. The length of the overhang of the septum secundum 54, which is the distance between superior aspect 53 and inferior aspect 55, increases towards the center portion of the septum secundum as shown.
The tunnel 58 between the right atrium 30 and left atrium 40 is defined by portions of the septum primum 52 and septum secundum 54 between the merger points 56a and 56p which have failed to fuse. The tunnel 58 is often at the apex of the septum secundum 54 as shown. When viewed within right atrium 30, the portion of the septum secundum 54 to the left of tunnel 58, which is referred to herein as the posterior portion 57p of the septum secundum, is longer than the portion of the septum secundum 54 to the right of tunnel 58, which is referred to herein as the anterior portion 57a of the septum secundum. In addition to being typically longer, the posterior portion 57a also typically has a more gradual taper than the anterior portion 57a as shown. The anterior pocket 59a is the area defined by the overhang of the anterior portion 57a of the septum secundum 54 and the septum primum 52, and it extends from the anterior merger point 56a toward the tunnel 58. Similarly, the posterior pocket 59p is the area defined by the overhang of the posterior portion 57p of septum secundum 54 and the septum primum 52, and it extends from the posterior merger point 56p toward the tunnel 58.
Conventional treatments for PFO, and other related conditions have generally involved invasive surgery, which also presents a risks to a patient. Although there are some less invasive treatments for PFO, such treatments have been less efficient at closing the PFO opening than techniques involving invasive surgery. One current method of correcting a PFO involves the use of an electrode for delivering RF energy to the tissue surrounding the PFO. Applying RF energy to the area around the PFO can weld the tissue together and damage the tissue to initiate tissue growth that joins both sides of the PFO opening. Unfortunately, existing RF PFO closure devices have not been capable of satisfactory closure, resulting in additional medical procedures, some of which are more invasive than the initial attempt to close the PFO.
Therefore, it would be advantageous to have an improved device or system and method of use that can be used in order to deliver the RF dose and/or determine the RF dose needed for treating a PFO. Additionally, it would be advantageous for the device or system to be configured to utilize catheter technology and anchors in order to deliver the RF dose locally to the tissue surrounding the PFO.